1. Field of the Invention
The present invention relates to a light pipe unit for converting light of a point light source efficiently into a plane light source to thereby make it possible to form a plane light source unit excellent in brightness and in its uniformity and to form a transmission type or reflection type liquid-crystal display device which is bright and easy to view.
The present application is based on Japanese Patent Applications Nos. Hei. 11-311917 and 353140, which are incorporated herein by reference.
2. Description of the Related Art
A side-lighting type plane light source unit having a light source disposed on a side surface of a light pipe having prism-like irregularities was heretofore known as a plane light source unit capable of forming a transmission type or reflection type liquid-crystal display device by use of a back-lighting or front-lighting system. Generally, a cold-cathode tube was used as the light source in such a plane light source unit. There was, however, a disadvantage that the cold-cathode tube was so large in consumed electric power that the frequency of required battery-exchanges was high when the plane light source unit was used portably.
In consideration of the above description, there was a proposal to arrange point light sources such as light-emitting diodes on an incidence side surface of a light pipe. Incidentally, the light-emitting diodes had advantages in reduction of consumed electric power, reduction of space and weight owing to use of no inverter, measures against electromagnetic wave, etc. From the point of view of prevention of disorder of a display image, improvement of light utilizing efficiency, etc., it was, however, difficult to incorporate a light scattering mechanism in the aforementioned light pipe. Hence, light was emitted like a stripe bright-line pattern corresponding to the location of arrangement of the point light sources. There was a problem that a large difference occurred between brightness and darkness to cause shortage of uniformity of brightness.
There was also a proposal to arrange a light-emitting diode on a side surface of a rod-like light pipe to thereby form a linear light source. The light-emitting diode was however needed to be positioned highly accurately on the incidence side surface of the light pipe in order to improve efficiency of incidence of light compared with the cold-cathode tube. Hence, a mechanism for holding the light-emitting diode was required, so that the number of parts was increased. There was a disadvantage that production efficiency ran short. Particularly in the case of a thin type light pipe, it was difficult to arrange the rod-like light pipe serving as a linear light source on the incidence side surface positionally accurately. Hence, when a light-emitting surface of the linear light source was connected to the incidence side surface of the light pipe so as to be integrated with the light pipe, uniformity of incidence of light was apt to be spoiled in a portion of connection between the light-emitting surface of the linear light source and the incidence side surface of the light pipe. Shade or emission line was apt to be produced. This was apt to cause lowering of display quality. If the contact area was reduced in order to prevent the lowering of display quality, the light pipe was apt to be ruptured because of shortage of strength. Particularly the connection portion was apt to become fragile. There was a disadvantage that the light pipe was hard to handle and was poor for practical use and that it was difficult to mass-produce the light pipe by injection molding, or the like.
An object of the present invention is to develop a light pipe unit capable of converting a point light source into a plane light source to thereby make it possible to form a plane light source unit excellent in brightness and in its uniformity and to form a transmission type or reflection type liquid-crystal display device which is bright and easy to view.
According to the first aspect of the present invention, there is provided a light pipe unit comprising: a surface light pipe including upper and lower surfaces and connected side surfaces constituted by an incident side surface formed between the upper and lower surfaces and side surfaces adjacent to the incident side surface; a linear light pipe including a light supply surface; the surface light pipe being connected to the linear light pipe through connected side surfaces and the light supply surface so that the linear light pipe converts incident light from a point light source into a linear light source and outputs the light of the linear light source through the light supply surface, and the surface light pipe converts incident light from the linear light source into a plane light source. There are further provided a plane light source unit wherein a point light source is disposed on a linear light pipe in the aforementioned light pipe unit, and a liquid-crystal display device comprising the plane light source unit and a liquid crystal cell.
According to the present invention, the surface light pipe and the linear light pipe are connected to each other through the connected side faces adjacent to the incidence side surface of the surface light pipe and the light supply surface of the linear light pipe. Variation in intensity of light incident on the surface light pipe through the connection portion can be suppressed to there by prevent production of shade or emission line. At the same time, the linear light pipe can be positioned highly accurately with respect to the incidence side surface of the surface light pipe so as to be arranged easily in a state excellent in efficiency of light incidence. Moreover, the resulting light pipe can be obtained as a light pipe unit easy to handle and of good practical use because the surface light pipe and the linear light pipe can be integrated with each other with a sufficient strength. Moreover, the resulting light pipe can be obtained as a light pipe unit that can be mass-produced by injection molding, or the like, because any mechanism-for holding the linear light pipe is not required so that the number of parts can be reduced.
As a result, light of a point light source is converted into a linear light source through the linear light pipe. The linear light source is further converted into a plane light source through the surface light pipe efficiently. Hence, a compact plane light source unit excellent in brightness and its uniformity and low in consumed electric power can be obtained. When the plane light source unit is used in a back-lighting or front-lighting system, a transmission type or reflection type liquid crystal display device which is bright, easy to view, excellent in display quality, low in consumed electric power and compact can be obtained with good production efficiency.
According to the second aspect of the present invention, there are provided: a light pipe unit comprising a linear light pipe for converting incident light from a point light source into a linear light source, and a surface light pipe for converting incident light from the linear light source into a plane light source, the linear light pipe and the surface light pipe being partially connected to each other; a plane light source unit wherein a point light source is disposed on the linear light pipe of the light pipe unit; and a liquid-crystal display device provided with at least the above-mentioned plane light source unit and a liquid crystal cell.
In the light pipe unit according to the present invention, light of a point light source is converted into a linear light source through the linear light pipe. The linear light source is further converted efficiently into a plane light source through the surface light pipe which is excellent in brightness and in its uniformity. When the plane light source unit is used in a back-lighting or front-lighting system, a transmission type or reflection type liquid crystal display device which is bright, and easy to view can be obtained.
Because the linear light pipe and the surface light pipe are partially connected to each other so as to be integrated with each other, the linear light source can be positioned highly accurately with respect to the incidence side surface of the surface light pipe. Hence, the linear light source can be disposed easily in a state excellent in efficiency of incidence of light. Moreover, it can be made unnecessary to provide separately any mechanism for holding the linear light pipe. Hence, the number of parts can be reduced. Hence, a plane light source unit or a liquid-crystal display device small in consumed electric power and compact in size can be obtained with good productivity.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.